1/*-
2 * Copyright (c) 2006 nCircle Network Security, Inc.
3 * Copyright (c) 2009 Robert N. M. Watson
4 * All rights reserved.
5 *
6 * This software was developed by Robert N. M. Watson for the TrustedBSD
7 * Project under contract to nCircle Network Security, Inc.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 *    notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 *    notice, this list of conditions and the following disclaimer in the
16 *    documentation and/or other materials provided with the distribution.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
22 * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
24 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
25 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
26 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
27 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
28 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31#include <sys/cdefs.h>
32__FBSDID("$FreeBSD: stable/11/sys/kern/kern_priv.c 339446 2018-10-20 16:20:36Z jamie $");
33
34#include <sys/param.h>
35#include <sys/jail.h>
36#include <sys/kernel.h>
37#include <sys/priv.h>
38#include <sys/proc.h>
39#include <sys/sdt.h>
40#include <sys/sysctl.h>
41#include <sys/systm.h>
42
43#include <security/mac/mac_framework.h>
44
45/*
46 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
47 * sysctl) determines whether the system 'super-user' policy is in effect.  If
48 * it is nonzero, an effective uid of 0 connotes special privilege,
49 * overriding many mandatory and discretionary protections.  If it is zero,
50 * uid 0 is offered no special privilege in the kernel security policy.
51 * Setting it to zero may seriously impact the functionality of many existing
52 * userland programs, and should not be done without careful consideration of
53 * the consequences.
54 */
55static int	suser_enabled = 1;
56SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RWTUN,
57    &suser_enabled, 0, "processes with uid 0 have privilege");
58
59static int	unprivileged_mlock = 1;
60SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
61    &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
62
63static int	unprivileged_read_msgbuf = 1;
64SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
65    CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
66    "Unprivileged processes may read the kernel message buffer");
67
68SDT_PROVIDER_DEFINE(priv);
69SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
70SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
71
72/*
73 * Check a credential for privilege.  Lots of good reasons to deny privilege;
74 * only a few to grant it.
75 */
76int
77priv_check_cred(struct ucred *cred, int priv, int flags)
78{
79	int error;
80
81	KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
82	    priv));
83
84	/*
85	 * We first evaluate policies that may deny the granting of
86	 * privilege unilaterally.
87	 */
88#ifdef MAC
89	error = mac_priv_check(cred, priv);
90	if (error)
91		goto out;
92#endif
93
94	/*
95	 * Jail policy will restrict certain privileges that may otherwise be
96	 * be granted.
97	 */
98	error = prison_priv_check(cred, priv);
99	if (error)
100		goto out;
101
102	if (unprivileged_mlock) {
103		/*
104		 * Allow unprivileged users to call mlock(2)/munlock(2) and
105		 * mlockall(2)/munlockall(2).
106		 */
107		switch (priv) {
108		case PRIV_VM_MLOCK:
109		case PRIV_VM_MUNLOCK:
110			error = 0;
111			goto out;
112		}
113	}
114
115	if (unprivileged_read_msgbuf) {
116		/*
117		 * Allow an unprivileged user to read the kernel message
118		 * buffer.
119		 */
120		if (priv == PRIV_MSGBUF) {
121			error = 0;
122			goto out;
123		}
124	}
125
126	/*
127	 * Having determined if privilege is restricted by various policies,
128	 * now determine if privilege is granted.  At this point, any policy
129	 * may grant privilege.  For now, we allow short-circuit boolean
130	 * evaluation, so may not call all policies.  Perhaps we should.
131	 *
132	 * Superuser policy grants privilege based on the effective (or in
133	 * the case of specific privileges, real) uid being 0.  We allow the
134	 * superuser policy to be globally disabled, although this is
135	 * currenty of limited utility.
136	 */
137	if (suser_enabled) {
138		switch (priv) {
139		case PRIV_MAXFILES:
140		case PRIV_MAXPROC:
141		case PRIV_PROC_LIMIT:
142			if (cred->cr_ruid == 0) {
143				error = 0;
144				goto out;
145			}
146			break;
147		default:
148			if (cred->cr_uid == 0) {
149				error = 0;
150				goto out;
151			}
152			break;
153		}
154	}
155
156	/*
157	 * Writes to kernel/physical memory are a typical root-only operation,
158	 * but non-root users are expected to be able to read it (provided they
159	 * have permission to access /dev/[k]mem).
160	 */
161	if (priv == PRIV_KMEM_READ) {
162		error = 0;
163		goto out;
164	}
165
166	/*
167	 * Now check with MAC, if enabled, to see if a policy module grants
168	 * privilege.
169	 */
170#ifdef MAC
171	if (mac_priv_grant(cred, priv) == 0) {
172		error = 0;
173		goto out;
174	}
175#endif
176
177	/*
178	 * The default is deny, so if no policies have granted it, reject
179	 * with a privilege error here.
180	 */
181	error = EPERM;
182out:
183	if (error)
184		SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
185	else
186		SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
187	return (error);
188}
189
190int
191priv_check(struct thread *td, int priv)
192{
193
194	KASSERT(td == curthread, ("priv_check: td != curthread"));
195
196	return (priv_check_cred(td->td_ucred, priv, 0));
197}
198